There is known WAVE (Wireless Access in Vehicular Environments) as a telecommunication standard used for an intelligent transport system as disclosed in Patent literature 1. WAVE uses two kinds of channels of a control channel and a service channel for a vehicular wireless communication apparatus and a roadside unit to communicate with each other.
The service channel is a channel used to transmit or receive the information for executing a service (i.e., service execution information, hereinafter). The service is provided as one of a plurality of kinds of services; the service channel is provided as one of a plurality of channels having mutually different frequencies. Each of the services is correspondingly associated with one of the service channels. Note that “information,” which may be used not only as an uncountable noun but also a countable noun, is equivalent to an informational item. One information is equivalent to one informational item; a plurality of informations are equivalent to a plurality of informational items.
The control channel is a channel used for a roadside unit to transmit the various information (i.e., service start information, hereinafter) for starting communication with a vehicular wireless communication apparatus via a service channel. The service start information is usually called WSA (Wave Service Advertisement).
To start the communication via a service channel, a reception channel used for reception by the vehicular wireless communication apparatus needs to be set to any one of the service channels. The WSA thus includes the information for identifying a service channel designated as a reception channel.
Further, while executing a service after starting the communication using the service channel, the WAVE usually alternates the service channel and the control channel in designating as the reception channel without fixedly designating the service channel as the reception channel.